1. Field of the Invention
The present invention relates to a liquid crystal display and driving method thereof, and in particular to a liquid crystal display and driving method thereof for rapidly charging pixel in the liquid crystal display.
2. Description of the Related Art
FIG. 1 is a unit circuit diagram of a conventional liquid crystal display. As shown in FIG. 1, the liquid crystal display comprises a common electrode COM10, a data line DL10, a scan line GL10, a thin film transistor (hereinafter referred to as “TFT”) Tx10, a storage capacitor Cst10, and a liquid crystal cell Clc10. The data line DL10 is coupled to a first terminal of the TFT Tx10, the scan line GL10 is coupled to a gate of the TFT Tx10, and the storage capacitor Cst10 is coupled between a second terminal of the TFT Tx10 and the common electrode COM10. In addition, a capacitor Cgd10 is a parasitic capacitor.
According to FIG. 1, in the conventional liquid crystal display, both the storage capacitor Cst10 and the liquid crystal cell Clc10 (equivalent to a capacitor) are coupled between the TFT Tx10 and the common electrode COM10. At a frame time, pixel voltage Vpx10 of the display unit varies within broad range, such that sufficient time is required for a voltage signal on the data line DL to charge the capacitors Cst10 and Clc10. A voltage level of the pixel voltage Vpx10 can accurately reach a voltage level corresponding to an image. However, as resolution of the liquid crystal display increases, charge time of the capacitors Clc10 and Cst10 decreases so that the pixel voltage Vpx10 cannot reach the voltage level corresponding to the image, degrading efficiency and quality of the liquid crystal display.
FIG. 2 is a timing chart of a conventional liquid crystal display unit. At a frame time Frt10 starting from time t2, voltage Vg10 of the scan line GL10 increases and the TFT Tx10 is turned on. Positive signal of the image, as compared with the common voltage on the common electrode COM10, on the data line DL10 is input to the liquid crystal cell Clc10 and the storage capacitor Cst10 via the TFT Tx10, and the pixel voltage Vpx10 increases. The pixel voltage Vpx10 varies by a full swing. At time t3, the voltage Vg10 decreases, the TFT Tx10 is turned off, and the capacitor Cgd10 couples the voltage Vg10 on the scan line GL10, resulting in a voltage drop of the pixel voltage Vpx10.
At time t5, the voltage Vg10 increases to turn on the TFT Tx10. Negative signal of the image, as compared with the common voltage on COM10, on the data line DL10 is input to the liquid crystal cell Clc10 and the storage capacitor Cst10 via the TFT Tx10, and the pixel voltage Vpx10 decreases. Similarly, the pixel voltage Vpx10 varies by a full swing. At time t6, the voltage Vg10 decreases to turn off the TFT Tx10, and the capacitor Cgd10 couples the voltage Vg10, resulting in a voltage drop on the pixel voltage Vpx10.
As described above, the swing of the voltage of the pixel in the conventional technology is large. Trends toward high resolution LCD devices and short charge time of pixels result in the problem of insufficient charging time of the pixel, such that there is a need to reduce the amplitude of pixel voltage swing during charging period, thereby more rapidly charging the pixel.